1. Field of the Invention
This invention relates generally to elevator systems that are particularly well adapted for use in tall buildings which systems occupy less building space and require less energy to operate than conventional elevator systems.
2. Description of Related Art
Currently, a block-shaped building, in which the area of floor space is the same from the ground floor to the top floor, has a practical height limit of slightly over 100 floors. This is because providing enough elevators to service passenger demand for the full floor space at higher floors would be impractical. In all tall buildings, almost the entire ground floor is used for elevators, waiting space, and access to them. A 100-story building would use up to 30 percent of the entire building floor space for elevators and waiting space. Because of the amount of space required, overall space used for elevators is extremely expensive, and any savings provided by a more efficient elevator system could create a substantial amount of useable, valuable, real estate.
Different methods have been suggested or tried to achieve a very efficient elevator system. To this end, different methods of operating the system have been employed including the "express" method wherein cars service the ground floor and different groups of upper floors. Another method is to increase the cruising speed to the maximum limit. Another is to use two-story, multicompartment, cars such as shown in U.S. Pat. No. 4,632,224.
The basic strategy for increasing efficiency is to reduce the round-trip time and/or increase the number of passengers carried on each trip. Although round-trip time may be reduced by minimizing the number of stops on a trip, this method may not be practical for real-world applications. If elevator cars are operated at high speeds, car vibration may become intolerable in a tall elevator shaft due to vibration of the drive ropes transmitted to the elevator car. Although two-story elevator cars can double the number of passengers carried on a trip, there will be a significant increase in round-trip time if both upper and lower compartments are allowed to stop at each floor. Also, passengers will be inconvenienced if the upper compartment is allowed to stop only at even numbered floors and the lower compartment at odd numbered floors.
Elevator systems that include a plurality of elevator cars in the same elevator shaft are well known as shown in applicant's U.S. Pat. No. 5,419,414. There, a counterweight is provided for each of the elevator cars. Also, elevator systems that include first and second elevator shafts are known, wherein elevator cars are moved upwardly in one shaft and downwardly in the other. Such a system is shown in U.S. Pat. No. 1,458,881 wherein endless chains for the support of elevator cars continuously travel up one shaft and down the other.